It has been known that blood coagulation includes both endogenous and extrinsic reactions and many coagulation factors participate in these reactions. And, accurate determination of their reactions in a sample is one of important items of clinical tests. However, many of these coagulation factors are protein and liable to be denaturated. Among them, particularly, V and VIII factors are known to be those readily inactivated. In many cases, instability of the factors causes trouble in clinical tests. For example, it has been said that a sample to be subjected to a coagulation test should be kept at 2.degree. to 8.degree. C. and the test should be done within 4 hours after blood collection. Further, a commercially available control plasma (lyophilized product) to be used in the test is stable for only one day under refrigeration after reconstitution thereof Stabilities of various coagulation factor deficient plasma to be used as test reagents are very low and many of them are stable for only several hours under refrigeration and should not be frozen.
If such unstable blood coagulation factors can be stabilized, it is possible to ease restriction of storage conditions and shelf life of a sample after blood collection, control plasma and various coagulation factor deficient plasma This is very advantageous in view of clinical tests as well as industrial purposes. Thus, there has been requested to develop a method for stabilizing blood coagulation factors.
On the other hand, many studies on stabilization of various proteins including enzymes have been done. However, substances which exhibit stabilization effects on proteins are quite different from each other according to kinds and origins of proteins and, at present, respective specific substances are independently found for stabilizing respective proteins.
Regarding stabilization of blood coagulation factors, there have been proposed coagulation factor preparations of certain factors, for example, VIII, IX and XIII factors, wherein these factors are stabilized by using albumin, dextran, sugars, amino acids, organic carboxylic acids and neutral salts such as NaCl, KCl and the like (Japanese Patent Kokai Nos. 56-127308, 56-135418, 58-74617, 59-134730, 60-199829, 61-60614, 62-10019 and 62-195331). However, they are aimed at stabilizing the coagulation factors during heat treatment for inactivation of viruses in the preparations and, therefore, they are added in very high concentrations. In a blood coagulation test, if such a substance, e.g., an amino acid such as glycine, alanine or the like is added to blood or plasma in a high concentration, for example, 10% or more, the coagulation reaction itself is inhibited and the desired coagulation test can not be carried out. Further, the above proposal is limited to only certain coagulation factors and the preparations do not contain many other blood components. Thus, the proposal is not directed to plasma or blood wherein all or a part of factors participated in coagulation reactions are contained or a part of them are deficient.
The present inventors have studied intensively to find out a method for stabilizing many blood coagulation factors contained in blood or plasma which does not unfavorably affect a coagulation reaction. As the result, it has been found that the coagulation factors can be remarkably stabilized by adding the dipeptide, glycylglycine and/or the tripeptide, glycylglycylglycine to blood or plasma.